1. Field of the Invention
The present invention relates to electronic equipment such as a video display terminal. Particularly, the present invention relates to electronic equipment constituted including plural control devices mutually connected via an internal bus.
2. Description of the Related Art
A conventional type video display terminal such as a television set for home use or for business use and a computer display is closed itself as one system, a slot for expanding a function is not provided as in a personal computer for example and a user cannot expand a necessary function freely. Therefore, if a function of a video display terminal is to be expanded, separate expanded equipment such as a video cassette recorder (VCR), a multiple sub-Nyquist sample encoding (MUSE) decoder and a scan converter (a converter of the synchronizing frequency of an input signal for corresponding to plural input video signals with a synchronizing frequency) is required to be prepared. Therefore, space for installing the expanded equipment is required to be provided newly. This is a common problem not only to a video display terminal but to the other electronic equipment for private use except an information processor such as a personal computer.
Also, the expanded equipment for the above conventional type electronic equipment is provided with an original user interface and is not constituted so that it is linked to the body of the electronic equipment except a part of simple functions. That is, the conventional type normal electronic equipment forms a closed system itself in which a master device (normally a microcomputer and others) which is the master of the system controls other plural slave devices via an internal bus and is not constituted so that the internal bus is extended to an external device. Therefore, in such a system, if the body of electronic equipment and expanded equipment use a slave device provided with the same specification (for example, a device for controlling a user interface device such as various operation keys and an indicator lamp), the same slave device is required to be installed in both equipment and it causes the increase of the cost. In this case, a method in which the body of the electronic equipment and the expanded equipment are connected via a serial channel for example and the expanded equipment uses the slave device via the master device of the body of the electronic equipment is also conceivable, however, in this method, a processing program for communication is newly required and there is a problem that processing becomes complicated as a whole because of communication.
Also, in a relatively small-scale electronic equipment system such as a conventional type video display terminal, a main microcomputer which is a master device controls a user interface and the stable operation of a system in any case and is constituted so that the main microcomputer is always operated as a master device. Therefore, to constitute a system on the premise that a predetermined function is extended later, a user interface program for supporting the extended function is required to be installed in the master device of the body of electronic equipment beforehand. However, for example, if a user uses the body of electronic equipment in which a user interface program which can correspond to an extended function is installed and desires the addition of another extended function later, the user interface program for the body of the electronic equipment is required to be changed to the contents which also supports the added function. Therefore, labor for changing or modifying a user interface program is required and the degree of freedom of the extension of a function is low.
To solve this problem, a method in which a user interface program which can support any presumed extended function is installed in the master device of the body of electronic equipment beforehand and even if any expanded equipment is connected, the above program can correspond to the expanded equipment immediately is conceivable. However, in this method, if presumed extended functions are many, the size of a user interface program for supporting all the extended functions is considerably large and the cost required for read only memory (ROM) for storing the user interface program is also increased. For a user who requires no extended function, the user interface program never used is installed and resources are wasted.
As described above, in the conventional type electronic equipment, as space for installing expanded equipment is required to be newly provided, a problem of arrangement may occur. As electronic equipment itself constitutes a closed system, there is a problem that the same slave device is required in both equipment if the body of electronic equipment and expanded equipment use a slave device provided with the same specification and the cost is increased. Further, when the degree of freedom and facility of the extension of a function are enhanced, a problem that the size of a user interface program and the cost are increased and resources are wasted occurs.